Multiple use concrete form liner

ABSTRACT

A multiple use, flexible, elastomeric liner for forms for concrete faced walls prepared by having a series of rigid panels in side by side relation, includes panels of liners for rigid panels having a concrete contacting face of a flexible, elastomeric synthetic polymer used throughout as a negative mold of a desired design in the finished concrete and having an opposed planar surface for face engagement with the form panels. The liner panels will not support the concrete for the wall without the backing panels. The elastomeric liner is a soft, flexible, resilient, elastomeric synthetic polymeric material which permits sharp relief designs having undercuts, and in edge engagement with similar panels squeeze together for a seamless surface in the completed concrete while leaving the impression of itself in exact detail in the hardened concrete.

This application is a .Iadd.reissue of Pat. No. 3,759,481 and a.Iaddend.continuation-in-part of copending application Ser. No. 17,423,filed Mar. 9, 1970, and now abandoned, for Flexible Liner for ConcreteForms.

Concrete forms, particularly for walls, partitions and the like,conventionally use rectangular panels of plywood, steel sheets, planks,and the like, supported by various types of reinforcing and supportmembers. When two or more of these panels are attached together inplanar alignment the form "in-total" is called a gang form and isusually stripped from hardened concrete as one piece rather than two ormore smaller pieces. The panels are generally held in side by siderelation, mounted on supporting structure, and generally two series ofsuch panels are mounted in generally parallel, spaced apart,face-to-face relation so that concrete may be poured between the two toeventually form the rectangular wall or partition. Plywood panels forsuch forms are generally 2 × 8 ft., or more commonly 4 × 8 ft. sheets.With the steel sheets, they are usually formed in 2-ft. widths mountedon the supporting structure for holding such panels in position forpouring a wall or partition. To keep the walls of the formssubstantially parallel under the weight of the concrete poured betweenthem, ties of wires, rods, or other material are fastened, through thespace into which the concrete is poured, from wall to wall, leaving theintervening wire or rod imbedded in the finished concrete. This, ofcourse, requires apertures or holes in the forms for the ties.

When the forms are made of plywood, the panels are generally coated withoil as a parting agent and in an attempt to prevent the penetration ofthe cement-loaded water into the wood of the panel. Long experience hasshown that such plywood panels rarely last more than four pours,particularly since the corners and edges are easily damaged in theerection, shipping and storing of the panels. In the reinforcing steelinstallation in the forms, numerous gouges and scratches are inflictedon the plywood from the sharp edges of the reinforcing bars and wire.The steel forms have a somewhat better life; however, they are quiteheavy and are easily bent and dented in the erection, storage and/ortransportation, so that after a few uses the panels can not make goodjoints with adjacent panels and the resulting concrete shows extrudedjoining lines and offset joints. With the plywood panels, cement waterdraining from the concrete enters the cracks of the joints and anydamaged surface areas of the panels and enters the plywood itself,causing deterioration of the plywood and warping of the plywood. Afterboth the plywood panels and steel panels have had several uses, thejoints between the panels become poorer and poorer and alignment becomesa definite problem. The produced concrete includes protruding andnon-aligned joints, which is particularly noticeable where there iswarping of the plywood panels and bending of the steel panels. Thesurface of the finished concrete assumes the surface of the form, whichis equivalent to a negative mold, and the surface of the finishedconcrete is generally from rough to smooth and includes all theblemishes of the panel formed in the concrete.

According to the present invention, there is provided a flexible,resilient form liner made of an elastomeric, synthetic polymericmaterial, which is castable or moldable and is easily fastened to thepanels of the concrete form. The liner has a concrete contacting surfaceof a desired design. The resilient material of the lining issufficiently soft to squeeze on adjacent liners under the weight of thewet concrete in the form, closing the joint lines between the liners sothat the finished concrete does not show joint lines. The liners arereadily attached to existing forms, or the existing forms are easilymodified to accept the liner. Depending on the nature of the attachingmethod chosen the elastomeric liners can be released from the concretestill attached to the form panel itself or they can be peeled after theform panel has been pulled and then reapplied to the panel ready for thenext pour of concrete. The form lining is readily placed on the formpanels with simple and varied means of holding the liners on the formpanels. After the concrete has cured, the liners are easily peeled orreleased from the concrete even with deep, base relief featuresincluding undercuts. The material is soft enough to readily free itself,without damage to the concrete, from the features of the designincluding the undercuts, and it is sufficiently strong so as to not tearin the removal process and therefore may be used over and over. Theelastomeric liner has a hardness sufficient to retain its design shapeeven under the weight of the concrete when the concrete is placed eithervertically or horizontally. A definite advantage of the flexible,resilient liners is that the face of the liners provides a negativeelastomeric mold of the desired wall design which may be of native rock,stone, striated wood, geometric or random patterns or any form desired.While the liner is quite soft, flexible and resilient, it is toughenough to maintain its integrity under the weight of the concrete in theconcrete form. It is sufficiently soft and flexible to squeeze againstan adjoining flexible liner to close the joints between the linersections. This prevents water from seeping through the liners, andretains the concrete within the form itself. The liners are useful overa long life, and it is not unusual to have the form panels last as longas the liners, which may range from 100 to 150 or more re-uses. Also, inusing the liners, it is preferable that the joint lines of the liners donot match the joint lines of the form panels, so that the joints of theliners are backed on a smooth surface of the form panel. It is sometimesdesirable to use a form release coating to help the liners in theremoving process.

The liners may be attached by any suitable means to the form panels. Thechoice of fastening means is determined by the composition of the formpanel itself, the thickness of the liner, and the design in the negativemold side of the liner. The process of making the form liners is,precast, site cast, poured in place, etc. Among the various forms ofattachment are lugs extending from the planar surface of the liner toextend through the concrete form panels, and these lugs are held in anyconvenient way. The lugs provide a means for sighting along a series ofsuch panels for correct alignment and to produce a very uniform wall.The liners may, also, be nailed, stapled, cemented, or otherwiseattached to the form panels.

The elastomeric synthetic polymer liners are inert to the chemicals ofthe concrete, whether the concrete is a conventional concrete or some ofthe new exotic concretes having various ingredients for varioushardening and fast setting purposes. This is obviously an improvementover rubber, or similar materials. The liner may be used in the concreteform with high cycle vibrators to muddle the concrete in the formswithout damage to the liner or to the form. This allows very finesurface detail in the hardened concrete surface while eliminating muchof the air entrapment generally associated with poured concrete. Theelastomeric polymer liner is not damaged if the high cycle vibratoraccidentally touches it in the vibrating process. The liner is softenough so that a slit in a liner permits the passage of the tie wire orrod, and the elastomeric polymeric plastic liner seals back around thetie in a gasketing action to form an excellent surface at theintersection of the tie with the finished concrete. Furthermore, theslits do not need to be filled or otherwise closed in subsequent re-usewhere there is no tie passing through the slit. The soft materialsqueezes together sealing the opening and thereby permits re-use of theform in different positions on concrete forms and with differentpositioning of the ties which pass through the liner.

It is, therefore, among the objects and advantages of the invention toprovide an elastomeric lining system for concrete forms which produce afine detail of predetermined design in the surface of finished pouredconcrete and also increases the life of the supporting concrete forms.

Another object of the invention is to provide a flexible, resilientconcrete form liner made of a synthetic plastic, elastomeric polymerwhich does not readily adhere to the concrete and is sufficiently softto be readily stripped from the form including the undercuts of thedesign of the mold without damage to the resulting concrete surface oritself.

A still further object of the invention is to provide a concrete formliner which provides a negative elastomeric concrete-contacting facemold with a predetermined pattern to produce a fine detail design in theresultant surface of the concrete structure.

These and other objects and advantages of the invention may be readilyascertained by referring to the following description and appendedillustrations in which:

FIG. 1 is a front elevational view of a portion of the concrete formliner according to the invention positioned against a concrete formpanel with a corner folded back;

FIG. 2 is a cross sectional detailed view of a form liner according tothe invention temporarily sealed on a portion of a concrete form panel;

FIG. 3 is a detailed view of the portion of a wall form showing thepositioning of the liner according to the invention in a concrete formfor a wall;

FIG. 4 is a plan view of a concrete form liner section according to theinvention illustrating the positioning of liners on concrete formpanels;

FIG. 5 is a cross sectional view of a form liner according to theinvention illustrating a longitudinal stabilizing member imbedded in theliner itself to reduce expansion and contraction without disturbing theelastomeric engaging face; and

FIG. 6 is a side elevational view of a section of a modified form lineraccording to the invention.

An elastomeric concrete form liner, according to the invention, may bemade of a soft, flexible, resilient, elastomeric synthetic polymericmaterial and may include such materials as .[.polyvinyl resins,.].silicone resins, polyethylene resins, polypropylene resins, .[.variousvinyl copolymers, polytetrofloro.]. .Iadd.polytetrafluoro.Iaddend.alkalines, polyesters, polyethers, and such similar syntheticresins; the hydrocarbon resins being generally considered saturated. Apreferred type of resin is a polyurethane resin which is provided with aparticular chain linkage in its chemistry to maintain the densepolyurethane soft, resilient, elastomeric and tough. The synthetic resinliner is manufactured by casting or molding in shallow, planar molds,usually having a minimum thickness of at least about 3/8 inch of linerto a thickness in excess of 4 or 6 or more inches. Since the liner is anegative mold for a desired configuration of surface, the thickness ofthe liner may vary throughout the extent of the panel from a minimumthickness to the maximum which represents the height between the lowestdepression and the highest elevation of the base relief of the finishedconcrete. To provide for a fine detail base relief of the finishedsurface, the liner must be flexible enough to permit undercuts in thefinished concrete whereby the liner may be pulled from the base reliefwithout breaking the concrete and without tearing the liner itself.Concrete has a tendency to shrink as it sets and the stretchable linerstill strips easily. It has been determined that a material having aShore A [ASTM hardness method D2240] of from .Badd..[.10 to 80, with apreferred range of.]..Baddend. 35 to 70, will have the desired softnessand flexibility for the liner. Below Shore A .Badd..[.10.]..Baddend..Iadd.35 .Iaddend.the material is too soft to maintain its integrityunder the weight of the concrete. This soft material flattens out andwill not give a reasonable or commercial reproduction of the desireddesign. Above Shore A .Badd..[.80.]..Baddend. .Iadd.70 .Iaddend.thematerial is too hard, losing its elasticity and flex, and attemptedremoval from the concrete surface will break the desired surface of theconcrete at undercuts, destroying the effect of the desired base relief,and also may damage the liner. The material should have a tensilemodulus of between 150 and 2,000 psi at 100 percent elongation [ASTMmethod at 23° C. D412]. The elongation at the same ASTM method D412should run from 100 to 175 percent at 23° C., providing for theflexibility necessary to perform as a negative mold for multiple use.The material having a tear strength in excess of 20 pounds per squareinch [ASTM method D624 Die C at 23° C.] prevents the rupture of materialbeing removed from the concrete product. The flexible, syntheticpolymeric plastic should have a tensile strength in excess of 100 poundsper square inch [ASTM method D412 at 23° C.] to provide a material whichwill maintain its integrity during the concrete pour and removal fromthe concrete surface. Concrete contains considerable amount of sand andgravel and sharp aggregate, and the plastic should have a high abrasionresistance so that it does not scratch or tear under the concrete pourinto the mold, and does not readily tear during erection or placement ofreinforcing steel. The Taber Abrasion test using 1,000 grams, 1,000cycles H-22 wheels, shows allowable loss from of frm 0.10 grams to 1.5grams.

The above properties define a soft, flexible, resilient, elastomericmaterial completely differentiated from the .[.rigid.]. lining materialsused to date. The liners show a commercial improvement in concreting notbefore used to attain the dramatic results obtainable with theinvention.

The liners of the invention are useful for concrete forms which may beformed for walls, partitions and the like in which a concrete form ismade of a plurality of side by side panels of such materials as plywood,steel and the like. Such concrete forms are useful for pre-cast concreteproducts, or for concrete products cast in situ, and they may includesuch pre-cast products as columns, beams, panels, various wallstructures and the like, and may be formed as castings for ceilings,floors and the like. The configuration, therefore, of the concrete moldin which the lining is to be used is determined by the use for which theparticular structure is to be used. In the casting of concretestructures, it frequently occurs that the forms for the particulararticle are quite large (gang form) and the lining of the invention ishighly useful and economical because it can be made in large sizes toform the particular gang form without any jointing and to minimize laborand handling at job site. The liners may be made in relatively smallstandard panels to line the forms for the finished articles. Thus, whilethe illustrations are directed to a liner for planar concrete forms,particularly upright walls, the concept of the use of the liner is notlimited to any concrete form but it is contemplated that the liner maybe used in any type of form for concrete or other cementous materialwhich sets or hardens with standing at ambient temperatures.

To obtain a simulated pattern in the set concrete, so as to make theconcrete appear in the shape of the simulated material and not requiringany further finishing other than perhaps painting, the concretecontacting face must be a soft, flexible, resilient, elastomericsynthetic polymeric plastic liner. A polymeric material which has ShoreA hardness of .Badd..[.10-80.]..Baddend. .Iadd.35-70.Iaddend., anelongation of 100-1,000 .Iadd.% .Iaddend.and tear strength in excess of20 pounds per .Iadd.square .Iaddend.inch is satisfactory for the liner.

The liner panel for the form of FIG. 1 illustrates a liner for forming asimulated barnwood [weathered wood] concrete wall. This concrete wallwill have the appearance, particularly when painted, of that of a wallformed of weathered boards, without the maintenance that would berequired of real barnwood, etc. A liner 10 formed of soft, resilient,flexible elastomeric synthetic polymeric plastic 10 is arranged with aface 12 formed as a negative elastomeric mold of the desiredconfiguration and a planar surface face 14 which is arranged to lie inface engagement with a concrete form panel 16. In the liner illustratedin FIG. 1, the panel of the liner includes raised portions 18 and 20which form depressions or lines simulating an open joint between boardsin the finished concrete. Also, included are simulated knot holes 22 andvarious raised grain in the boards actually simulating the surfaceeffect of barnwood. The surface may include circular depressions 24, 26,for example, which produce slight knobs on the finished concrete surfaceindicating nail heads such as might be found in old barnwood. Theundercutting is obviously a tremendous asset to the total "look" of thefinished concrete.

The liner is formed by casting or molding or curing liquid polyurethaneprecursors, or other suitable precursors for synthetic polymers, in ashallow planar mold which has the positive of the desired design in thebottom of the mold. The mold for the liner may be elastomeric itself soas to further enhance the detail obtainable. It may, also, be of a rigidmaterial such as set concrete or aluminum, etc., and may use external orinterior heating sources to accelerate the chemical action that curesthe elastomeric liner material into a tough elastomeric sheet. Thepolyurethanes are generally poly-functional long chain alcohols with aplurality of hydroxyl groups reacted with a polyisocyanate. Thepolyurethanes themselves are esters of dicarbamic acids and glycols, orinter-molecular esters of gamma-hydroxic carbamic acids. Thepolyurethane elastomers are made from diisocyanates, aliphaticpolyesters, etc. Several types of polyurethanes are commerciallyavailable as 2 part pourable liquids, which have a good shelf life andare easily mixed with the necessary polymerizing or curing agent. Oneform is a polyester made from ethylene and propylene glycols with adipicacid. A curing agent such as toluene, naphthylene or diphenylmethanediisocyanates may be used. The resultant polymer should have thehardness, tensile modulus, elongation, tear strength, tensile strengthand abrasion resistance in the ranges set forth above for forming theliner of invention. One of the specific liners manufactured by theassignee at present invention .[.is called "Red Flex", which is acolored polyvinyl plastisol which has a Shore A hardness of 47-32,tensile modulus of 175-368, elongation of 820-460 percent, a tearstrength of 62-102 and a tensile strength of 810-1,200. Another specificliner.]. is a polyurethane called "Flexliner" having a Shore A hardnessof 53- 56, a tensile modulus of 212-234 .IaddψIaddend., an elongation of270-300 .Iadd.% .Iaddend.tear strength of 67-73 .Iadd.psi .Iaddend.and atensile strength of 504-563 .IaddψIaddend. .

In many base relief designs which may be desired, an uncercut in thefinished product is necessary to give the fine detail desired. As shownin FIG. 2, a liner 10a includes a series of undercuts 30a, 30b, as wellas elevated lands, 32a, 32b and 32c. The liner 10a is attached by anyconvenient means to a concrete form panel 16. The thickness x which isthe minimum thickness of any portion of the liner should be at leastabout 3/8 inches which will provide the liner with sufficient integrityto maintain its strength in its thinnest sections. It is noted that thehigher lands produce a substantial thickness of the liner. Various typesof base relief may include portions of the liner which exceed athickness of 4, 6 or more inches, again depending on the type of baserelief which is desired in the finished concrete. It is obvious that theelastomeric liner may be smooth with no detail on the concretecontacting face. This allows the user to take advantage of many of itsbenefits such as non-absorbing of cement water, gasketing at tie holes,lining curved or odd-shaped forms, insulating, etc. These qualities allcontribute to a smooth, well-cured and unstreaked concrete wall orfloor. Until now only rigid type liners have been commericallyavailable. The invention attains a high level of sophistication andversatility in concreting.

In using the form of the invention, as shown in FIG. 3, a pair ofconcrete form panels 35 and 36 are arranged in parallel spaced relationto each other, and a pair of liners 37 and 38 are shown secured to panel35 with the negative elastomeric face mold section facing inwardly ofthe parallel concrete forms to produce, on the face adjacent to panel35, the positive of the desired base relief configuration. As is wellknown, in the concrete wall construction the panels of the concrete formare held in parallel position by a plurality of ties which may be wire,rod, or the like, which extend through both of the parallel concretepanels and are imbedded in the finished concrete. To remove the concreteforms from the finished concrete the ties must be cut to permit theremoval of the form from the cured concrete. Furthermore, to permit theties to pass through the concrete forms, holes must be formed in theform that are big enough to allow passage of the head of the tie, whichhas a greater circumference than does the shank or tie itself. This, ofcourse, permits concrete-laden water and some of the concrete itself toooze out of the holes if they are not packed or gasketed from theoutside of the form itself. Visual inspection of conventionally formedconcrete walls shows just how unsatisfactory this can be. Withapplicant's soft, resilient liner, however, the ties may be merelypassed through slits which stretch to accomodate the tie head, formed inthe liner at the necessary locations. The material of the liner itselfwill squeeze down on the shank of the tie preventing any oozing ofconcrete or water through the opening through which the tie passes. Thisforms a very smooth joint for the concrete form tie. In addition, whenthe form is used in the next location on a different wall form, a tiedoes not necessarily have to pass through the same slits, since thematerial will squeeze on itself sealing the slits, causing no blemish onthe finished concrete surface.

Preferably, the liners are arranged in abutting position on the concreteforms with their joints in the middle of the form panel rather than onthe joints of the form panel to provide a good backing for the linerjoints. This is desirable, but not essential. Since the liner itselfwill not support the heavy concrete which is poured therein,misalignment of the joints of the concrete forms will be covered by theliner. As shown in FIG. 3, a series of three concrete form panels 40, 41and 42 are arranged in side by side abutting position, and liner panels43, 44, 45 and 46 are arranged thereon. The abutting joints between eachof the liner panels are in the middle of the concrete panels rather thanon the joint lines. Thus the joint 50 between panels 43 and 44 are inthe middle of panel 40 rather than on the joint 51 between concretepanel 40 and 41. In a similar manner joint 52 between the liner panels44 and 45 are in the middle of panel 41. This provides good backing forthe edge abutting joints of the panels. As pointed out above, thematerial is sufficiently soft that it squeezes together completelyclosing the joint and forming a seamless surface of the finishedconcrete. It is obvious that the elastomeric liners can be placed withjoints abutting over joints in the form but good concreting practicesdictate the system detailed herein.

As shown by the physical properties of the desired concrete form linersheets the synthetic polymer plastic material is soft, flexible, andresilient, to allow for the fine detail obtainable from poured concreteand yet be easily stripped. It is known that all elastomeric materialshave coefficients of liner expansion and contraction under conditions ofheat and cold. The synthetic polymeric liner may be stabilized so as tocontrol this effect in applications where it is required for goodresults. It is obvious that a steam-heated precast bed can attaintemperature approaching 200° F. Concrete itself can approach 140° F. asit takes its set. In summertime or hot weather concreting, this heatgeneration plus the hydration process plus the ambient temperature cangenerate higher temperatures in the concrete against the plymeric lineritself. By imbedding a perforated sheet, screen, cloth or film into theliner at the time of manufacture (before the precursors change from aliquid to an elastomer sheet) a plane of stabilization can be added tothe liner. When a perforated sheet is used, the perforations act asindividual stabilizing points, usually 1 inch on center throughout theentire planar surface of the elastomeric liner. Since the elastomericmaterial either completely surrounds the stabilizing sheet or at leastflows to the top of each perforation and bonds totally to the entiresheet, the elastomeric face engagement side of the liner is not affectedand will still stretch and bend and flex from detail and undercuts onset concrete. The tie holes are still slit in the surface but theimbedded stabilizing sheet must be drilled the same circumference as thetie head for it to pass through, but the liner slit still stretches andcloses on the shank to obtain the gasketing action. It is preferred touse as a stabilizing element a material that has a very low coefficientof expansion and contraction as well as a low moisture content, since atelevated temperatures water vapor gas may form during liner curing andexpand, causing difiguration and degradation of the element andsurrounding elastomeric material. It is obvious that other stabilizerscould be imbedded in or glued to the liner providing the same degree oflateral stability when required. Such materials are hardware cloth,glass fiber strands or webs, perforated metal films, perforated plasticfilms or sheets, screening or the like may be used. Expansion and/orcontraction has always been a problem in any concrete form liner sincethe negative face can be distorted, thus making the concrete surfacedistorted or out of line, etc. The addition of the lateral stabilizingsheet which is perforated or absorbent (as in glass matting) correctsthis deficiency when required in the elastomeric concrete form liner ofthis invention.

It is known that the liners absorb or reflect radiant or convective heator cold at different rates. The more heat absorbed the greaterexpansion, etc. By the addition of a light reflective color "white" tothe elastomeric material, the concrete liner becomes itself a reflectorof heat. Since reflection will occur the liner itself does not becomeoverly heated, thus reducing expansion or contraction. It is obviousthat this is desirable in many instances where the stabilizer sheet isnot suitable to the application. Also, both white color and a stabilizercould be used to attain even a greater degree of stability. White orlighter type colors are, also, desirable so the user of the elastomericliner is more able to see any dirt or refuse that may be on the linerbefore concrete is placed against it, causing a speckled or dirtyappearance on the set concrete surface. It is not common commercialpractice to add white pigment to the preferred urethane elastomer.However, because of its inherent heat reflective qualities it isdesirable for the addition in the synthetic polymeric liner ofinvention. It is obvious that other colors may be added foridentification of product by both sellers and customers of said liners.

Another important function of the invention is to provide a vaporbarrier far superior to plain plywood. Concrete in the curing processmust retain most of the original water content of the mix, otherwise theparticles of cement will not hydrate and adequately bond together andthe concrete will not attain acceptable strength. In hot weatherconcreting, it is especially important to protect the wet concrete fromlosing too much moisture. General practice is to have burlap sacksdraped over forms after a concrete pour and a worker keeping the sacksand the forms wet with a hose. Evaporation will rob the water from thewet concrete right through the plywood or wood form if this procedure isnot followed, and this could be disastrous to the pour. When theconcrete form is lined with the elastomeric liner of invention themoisture vapor can not escape from the concrete through the forms. Theinsulating value of the elastomeric liner is far superior to wood orsteel and other currently available thin section rigid concrete formliners. Insulation is needed even in summertime to keep too much heatout of the concrete. In some cases curing blankets are actually thrownover wet concrete to this end. Too much heat obviously causes theevaporation process to increase. For wintertime concreting, the samecuring blankets are sometimes thrown over the wet concrete to retain thegenerated heat therein. The elastomeric liner of invention, being atleast 3/8 inch thick at its median thickness, acts as an insulator tohold the heat. If it becomes necessary to actually put heat into the wetconcrete to maintain its curing temperature, electrical heating tapesmay be imbedded in the elastomeric liner much as the stabilizing sheetis to accomplish this end without affecting the elastomeric concretecontacting face of the liner of invention. Heated, rigid, forms havebeen used extensively for many years but they are expensive and do notallow for the fine detail and undercutting available in the syntheticpolymeric elastomeric liner of invention.

A heating cable or tape, in the form of interconnecting mesh, may formof type of stabilizing sheet within the elastomer liner as it providesthe heat source necessary to reverse the heat flow in cold weatherconcreting. Also, a coolant could be circulated through small tubesimbedded in the liner of invention to help in hot, summertimeconcreting.

As shown in FIG. 6, a portion of a liner 70 has electric resistancewires 71 embedded in the plastic material, and power leads 72 and 73 areconnected therewith. This provides a heating mat for liner. A plug 74indicates attachment to a power source. The resistance wires may bereplaced by small tubes which form a heat exchange duct through theliner. Through the tubes heating or cooling liquid may be circulated fora desired temperature treatment.

I claim:
 1. In combination with large smooth surfaced panels forconcrete forms for structural members, a multiple use liner comprising asheet of soft, flexible, resilient, elastomeric synthetic polymermaterial which is inert to concrete and having a generally smooth rearsurface in face contact with said large smooth surfaced panels, saidsheet being formed independently of said panels and supported thereby;the opposite face of said liner having a concrete contacting face formedas a negative mold including undercuts of a desired pattern on the setconcrete; said sheeting being at least about 3/8 inch thick at itsthinnest section; said sheet having a hardness of from.Badd..[.10-80.]..Baddend. .Iadd.35-70 .Iaddend.Shore A, which permitssaid material to be deformed without damage for releasing from thedesigns in the set concrete and having an elongation of from 100-1,000percent at a tensile modulus of from 150-2,000 psi at 100 percentelongation, a .[.tensile.]. .Iadd.tear .Iaddend.strength in excess of 20pounds per .Iadd.square .Iaddend.inch, whereby said liner may be removedfrom a design in set concrete without damage to the concrete includingundercuts in the design and said liner squeezes against an adjacentliner under the weight of contained concrete to seal the joint linetherebetween and seal around ties or the like passing through the liner.2. The combination of claim 1 wherein said polymeric material is apolyurethane having a Shore A hardness of about 53-56, tensile modulusof 212-234 .IaddψIaddend. , elongation of 270-300 percent, tear strengthof 67-73 .Iadd.psi .Iaddend.and a tensile strength of 504-563.IaddψIaddend. . .[.3. The combination of claim 1 wherein said polymericmaterial is a polyvinyl chloride having a Shore A hardness of about47-32, tensile modulus of about 175-368, elongation of 320- 460 percent,a tear strength of 62-102 and a tensile strength of about 810-1,200..].4. The combination of claim 1 wherein said sheet essentially covers thearea of said panels forming a moisture and temperature barrier forconcrete thereagainst.
 5. The combination of claim 4 wherein said sheethas its full negative mold face in a desired pattern imparting a totalsimulated look of the desired configuration to a concrete face setthereagainst.
 6. The combination of claim 1 wherein said sheet is formedwith a light colored pigment as a reflector for heat into and out ofconcrete in engagement therewith.
 7. The combination of claim 1 whereinsaid sheet is sufficiently soft and sufficiently thick to produce agasketing effect around a tie passed through a slit therein.
 8. Thecombination of claim 1 wherein said sheet has a heating element imbeddedtherein for heating contained concrete.
 9. The combination of claim 1wherein said sheet has a heat exchanger tubing imbedded therein forheating or cooling said sheet.